Radial velocity curve of the HD170582 donor

Based on the study of the ASAS V-band light curve, we determine an improved orbital period of 16.87177+/-0.02084 d and a long period of 587 d. We disentangled the light curve into an orbital part, determining ephemerides and revealing orbital ellipsoidal variability with unequal maxima, and a long cycle, showing quasi-sinusoidal changes with amplitude {Delta}V=0.1mag.

Assuming synchronous rotation for the cool stellar component and semidetached configuration we find a cool evolved star of M_2_=1.9+/-0.1 M_{sun}_, T_2_=8000+/-100 K and R_2_=15.6+/-0.2 R_{sun}_, and an early B-type dwarf of M_1_=9.0+/-0.2 M_{sun}_. The B-type star is surrounded by a geometrically and optically thick accretion disc of radial extension 20.8+/-0.3 R_{sun}_ contributing about 35 percent to the system luminosity at the V band.